1. Field of the Invention
This invention relates to a solvent for use in making pressure-sensitive manifold paper and more specifically to a solvent for dyes as the materials for microcapsules of pressure-sensitive manifold paper.
2. Description of the Related Art
The initial solvent for the solvent for microcapsules was polychloro biphenyl, the production of which was terminated due to the problem of environmental pollution. Among the solvents currently available in the market are alkyl naphthalene (Japanese Patent Disclosure Nos. 47-41908 through -41914 and Japanese Patent Publication No. 49-5928), diallyl ethane (Japanese Patent Disclosure No. 47-31718, Japanese Patent Disclosure No. 47-26213, Japanese Patent Publication No. 49-2126), alkyl biphenyl (Japanese patent Publication No. 49-21608, Japanese Patent Disclosure No. 47-8665 and Japanese Patent Disclosure No. 47-22212), hydrogenated terphenyl (Japanese Patent Publication 49-2125, Japanese Patent Disclosure No. 48-92112, corresponding to U.S. patent application No. 225,658), and triallyl diethane (Japanese Patent Publication No. 49-8289, Japanese Patent Disclosure No. 47-26214, Japanese Patent Disclosure No. 48-86614). The solvents, the development of which are now under way, include tetralin derivatives.
In practical use, these solvents are used after diluted with a petroleum fraction such as kerosine, naphtha and paraffin or a synthetic oil such as chlorinated paraffin and chlorinated biphenyl or animal oil, vegetable oil, or mineral oil. The dilution is done for the purpose of cost reduction.
The required conditions of the solvent are as follows.
1. Dissolves leuco dyes as color formers at high concentrations. PA1 2. Has a high boiling point and does not evaporate in the thermodrying process or in an environment of high temperature. PA1 3. Does not dissolve into water in the capsulation process. PA1 4. Does not disensitize the color formers or inhibit their action on the lower sheet of the pressure-sensitive manifold paper. The word "disensitize" here means deteriorating the developing capacity of the developer or making the developer lose its capacity. PA1 5. Has a high adsorptive affinity with the developer, that is, color-reactive substances and thereby contributes to favorable color development. PA1 6. Has excellent resistance to acids and alkalis and is stable chemically. PA1 7. Has a viscosity low enough to allow the dye to freely seep from the capsule wall and has a very little rise in viscosity even at low temperatures. PA1 8. Is colorless or has a very light color. PA1 9. Has no disagreeable smell. PA1 10. Has a low toxicity.
Some of the solvents currently sold in the market have a boiling point from 280.degree. to higher than 300.degree. C., a flow point of lower than about -30.degree. C. and a kinematic viscosity of less than 10 cp at 25.degree. C. These solvents meet the requirements of 2 and 7 above, do not pose a problem of environmental pollution, help improve the copying speed and enable their use in the frigid regions.
Those commercial products are the solvents containing non-condensed or condensed polycyclic compounds having the alkyl groups and hydrogen groups and which therefore are manufactured by employing a complicated reaction path.
The solvency of these commercial solvents to the black leuco dye is 3.5 wt % and that of the commercial solvents to the blue leuco dye is about 10 wt %. The solvent users call for solvents with a high solvency for various dyes, that is, a solvency of 7 to 10 wt % for a black dye for example. The reason is as follows. The solvent is blended in the subsequent process with a diluting agent. For dissolution of a leuco dye by a solvent before this blending, the users want to use a solvent having a highest possible dissolving power for leuco dyes.